It is well known to connect electrical leads to a pinch or press seal in a lamp. When using high silica containing glass in which, for example, the silicon oxide proportion is at least 96% - by weight, foils, for example of molybdenum, are melted into the press or pinch seal.
The technology of vacuum-tight melt connection of electrical supply leads through a pinch or press seal and into a bulb by use of foils is applied, primarily, in halogen incandescent lamps and in metal halide discharge lamps. Usually, the bulbs are made of quartz glass and the foils are made of molybdenum.
The tightness of the melt connection between the molybdenum and quartz glass can be improved by an intermediate
layer. It has been proposed to coat the molybdenum foil with a layer of chromium to protect the molybdenum foil against oxidation, see, for example, U.S. Pat. No. 3,420,944. It has also been proposed to use an intermediate connectng solder glass, for example including leadphosphorus- oxide, see British Pat. No. 1,485,378. Substantial differences in thermal coefficients of expansion between molybdenum and quartz can be alleviated by interposition of one or more intermediate layers of glass having high boron oxide content, with coefficients of expansion between the extremes of the molybdenum and the quartz glass see French Pat. No. 961 730. The thermal coefficient of expansion of molybdenum is about 50.multidot.10.sup.-7 /.sup. K; that of quartz glass 7.multidot.10.sup.-7 /.sup. K.
Vapor-depositing thin metal layers is costly both with respect to material requirements as well as apparatus and technological requirements of the process of vapor deposition. Lead-phosphorus-oxide is not suitable for high temperatures and, thus, cannot be readily used in halogen incandescent lamps or metal halide discharge lamps, which operate at high bulb and internal temperatures, typically in the order of several hundred degrees C. Intermediate glass layers which have been proposed to ameliorate the differences in thermal coefficients of expansion are also not suitable for high temperatures. Application of a plurality of intermediate layers, with respectively different thermal coefficients of expansion, is very costly. Such glasses may include boron oxide.